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Last Modified: Sat May 14 16:36:12 UTC 2011
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<p>
<a href="index.html">[Back to PDFMiner homepage]</a>

<h1>Programming with PDFMiner</h1>
<p>
This page explains how to use PDFMiner as a library 
from other applications.
<ul>
<li> <a href="#overview">Overview</a>
<li> <a href="#basic">Basic Usage</a>
<li> <a href="#layout">Layout Analysis</a>
<li> <a href="#tocextract">TOC Extraction</a>
<li> <a href="#extend">Parser Extension</a>
</ul>

<h2><a name="overview">Overview</a></h2>
<p>
<strong>PDF is evil.</strong>  Although it is called a PDF
"document", it's nothing like Word or HTML document. PDF is more
like a graphic representation.  PDF contents are just a bunch of
instructions that tell how to place the stuff at each exact
position on a display or paper.  In most cases, it has no logical
structure such as sentences or paragraphs and it cannot adapt
itself when the paper size changes. PDFMiner attempts to
reconstruct some of those structures by guessing from its
positioning, but there's nothing guaranteed to work. Ugly, I
know. Again, PDF is evil.

<p>
[More technical details about the internal structure of PDF:
"How to Extract Text Contents from PDF Manually"
<a href="http://www.youtube.com/watch?v=k34wRxaxA_c">(part 1)</a>
<a href="http://www.youtube.com/watch?v=_A1M4OdNsiQ">(part 2)</a>
<a href="http://www.youtube.com/watch?v=sfV_7cWPgZE">(part 3)</a>]

<p>
Because a PDF file has such a big and complex structure,
parsing a PDF file as a whole is time and memory consuming. However,
not every part is needed for most PDF processing tasks. Therefore
PDFMiner takes a strategy of lazy parsing, which is to parse the
stuff only when it's necessary. To parse PDF files, you need to use at
least two classes: <code>PDFParser</code> and <code>PDFDocument</code>.  
These two objects are associated with each other.
<code>PDFParser</code> fetches data from a file,
and <code>PDFDocument</code> stores it. You'll also need
<code>PDFPageInterpreter</code> to process the page contents
and <code>PDFDevice</code> to translate it to whatever you need.
<code>PDFResourceManager</code> is used to store
shared resources such as fonts or images.

<p>
Figure 1 shows the relationship between the classes in PDFMiner.

<div align=center>
<img src="objrel.png"><br>
<small>Figure 1. Relationships between PDFMiner classes</small>
</div>

<h2><a name="basic">Basic Usage</a></h2>
<p>
A typical way to parse a PDF file is the following:
<blockquote><pre>
from pdfminer.pdfparser import PDFParser, PDFDocument
from pdfminer.pdfinterp import PDFResourceManager, PDFPageInterpreter
from pdfminer.pdfdevice import PDFDevice

<span class="comment"># Open a PDF file.</span>
fp = open('mypdf.pdf', 'rb')
<span class="comment"># Create a PDF parser object associated with the file object.</span>
parser = PDFParser(fp)
<span class="comment"># Create a PDF document object that stores the document structure.</span>
doc = PDFDocument()
<span class="comment"># Connect the parser and document objects.</span>
parser.set_document(doc)
doc.set_parser(parser)
<span class="comment"># Supply the password for initialization.</span>
<span class="comment"># (If no password is set, give an empty string.)</span>
doc.initialize(password)
<span class="comment"># Check if the document allows text extraction. If not, abort.</span>
if not doc.is_extractable:
    raise PDFTextExtractionNotAllowed
<span class="comment"># Create a PDF resource manager object that stores shared resources.</span>
rsrcmgr = PDFResourceManager()
<span class="comment"># Create a PDF device object.</span>
device = PDFDevice(rsrcmgr)
<span class="comment"># Create a PDF interpreter object.</span>
interpreter = PDFPageInterpreter(rsrcmgr, device)
<span class="comment"># Process each page contained in the document.</span>
for page in doc.get_pages():
    interpreter.process_page(page)
</pre></blockquote>

<h2><a name="layout">Accessing Layout Objects</a></h2>
<p>
Here is a typical way to use the layout analysis function:
<blockquote><pre>
from pdfminer.layout import LAParams
from pdfminer.converter import PDFPageAggregator

<span class="comment"># Set parameters for analysis.</span>
laparams = LAParams()
<span class="comment"># Create a PDF page aggregator object.</span>
device = PDFPageAggregator(rsrcmgr, laparams=laparams)
interpreter = PDFPageInterpreter(rsrcmgr, device)
for page in doc.get_pages():
    interpreter.process_page(page)
    <span class="comment"># receive the LTPage object for the page.</span>
    layout = device.get_result()
</pre></blockquote>

The layout analyzer gives a "<code>LTPage</code>" object for each page
in the PDF document. The object contains child objects within the page,
forming a tree-like structure. Figure 2 shows the relationship between
these objects.

<div align=center>
<img src="layout.png"><br>
<small>Figure 2. Layout objects and its tree structure</small>
</div>

<dl>
<dt> <code>LTPage</code>
<dd> Represents an entire page. May contain child objects like
<code>LTTextBox</code>, <code>LTFigure</code>, <code>LTImage</code>, <code>LTRect</code>, 
<code>LTCurve</code> and <code>LTLine</code>.

<dt> <code>LTTextBox</code>
<dd> Represents a group of text chunks that can be contained in a rectangular area.
Note that this box is created by geometric analysis and does not necessarily
represents a logical boundary of the text. 
It contains a list of <code>LTTextLine</code> objects.
<code>get_text()</code> method returns the text content.

<dt> <code>LTTextLine</code>
<dd> Contains a list of <code>LTChar</code> objects that represent
a single text line. The characters are aligned either horizontaly
or vertically, depending on the text's writing mode.
<code>get_text()</code> method returns the text content.

<dt> <code>LTChar</code>
<dt> <code>LTAnon</code>
<dd> Represent an actual letter in the text as a Unicode string.
Note that, while a <code>LTChar</code> object has actual boundaries,
<code>LTAnon</code> objects does not, as these are "virtual" characters,
inserted by a layout analyzer according to the relationship between two characters
(e.g. a space).

<dt> <code>LTFigure</code>
<dd> Represents an area used by PDF Form objects. PDF Forms can be used to
present figures or pictures by embedding yet another PDF document within a page.
Note that <code>LTFigure</code> objects can appear recursively.

<dt> <code>LTImage</code>
<dd> Represents an image object. Embedded images can be 
in JPEG or other formats, but currently PDFMiner does not 
pay much attention to graphical objects.

<dt> <code>LTLine</code>
<dd> Represents a single straight line.
Could be used for separating text or figures.

<dt> <code>LTRect</code>
<dd> Represents a rectangle.
Could be used for framing another pictures or figures.

<dt> <code>LTCurve</code>
<dd> Represents a generic bezier curve.
</dl>

<p>
Also, check out <a href="http://denis.papathanasiou.org/?p=343">a more complete example by Denis Papathanasiou</a>.

<h2><a name="tocextract">TOC Extraction</a></h2>
<p>
PDFMiner provides functions to access the document's table of contents
("Outlines").

<blockquote><pre>
from pdfminer.pdfparser import PDFParser, PDFDocument

fp = open('mypdf.pdf', 'rb')
parser = PDFParser(fp)
doc = PDFDocument()
parser.set_document(doc)
doc.set_parser(parser)
doc.initialize(password)

<span class="comment"># Get the outlines of the document.</span>
outlines = doc.get_outlines()
for (level,title,dest,a,se) in outlines:
    print (level, title)
</pre></blockquote>

<p>
Some PDF documents use page numbers as destinations, while others
use page numbers and the physical location within the page. Since
PDF does not have a logical strucutre, and it does not provide a
way to refer to any in-page object from the outside, there's no
way to tell exactly which part of text these destinations are
refering to.

<h2><a name="extend">Parser Extension</a></h2>

<p>
You can extend <code>PDFPageInterpreter</code> and <code>PDFDevice</code> class
in order to process them differently / obtain other information.

<hr noshade>
<address>Yusuke Shinyama</address>
</body>
